There are many prior art devices relating to various types of valves permitting the drainage of fluid for the treatment of hydrocephalus. However, these prior art devices are all used for the treatment of the already born, and are not suitable for the treatment of a hydrocephalic fetus. Examples of such prior art devices are shown in the following prior U.S. patents, found as a result of a preliminary search:
Holter et al, U.S. Pat. No. 2,969,066, Schwartz, U.S. Pat. No. 3,109,429, Hakim, U.S. Pat. No. 3,288,142, Kuffer et al, U.S. Pat. No. 3,674,050, Hakim, U.S. Pat. No. 3,924,635, Hakim, U.S. Pat. No. 4,106,510, and Hildebrandt et al, U.S. Pat. No. 4,156,422.